Vegetable oils are obtainable in large volumes from renewable resources and in general are characterized as readily biodegradable or "environmentally friendly". As a result, such oils and related unsaturated polyol fatty acid ester stocks are potentially attractive for use in a wide variety of applications.
With respect to use for lubrication purposes, especially as machine lubricants, vegetable oils have not been fully desirable. Many vegetable oils do not possess the desired spectrum of characteristics relating to: pour point; oxidative stability; and compatibility with additives among others. Vegetable oils do however possess many desirable properties for use as a lubricant. In particular, vegetable oils typically provide good boundary lubrication, good viscosity, high viscosity index and high flash point. In addition, vegetable oils are generally nontoxic and readily biodegradable. For example, under standard test conditions (e.g., OCED 301D test method), a typical vegetable oil can biodegrade up to 80% into carbon dioxide and water in 28 days, as compared to 25% or less for typical petroleum-based lubricating fluids.
Two characteristics, which are often major limitations to the utilization of vegetable oils as lubricants, relate to stability and low temperature behavior. In particular, vegetable oils often contain substantial amounts of unsaturation (i.e., one or more carbon--carbon double bonds distributed along the fatty acyl chains). The sites of unsaturation may be associated with sufficient oxidative reactivity to render the oils insufficiently stable for use as lubricants. If efforts are made to reduce the unsaturation, for example by hydrogenation, generally undesirable changes in pour point and/or viscosity index result.